1. Field of the Invention
The present invention relates to a signal frequency band detection device used in a wireless receiver for detecting a frequency band of signals received by the wireless receiver.
2. Description of the Related Art
In a wireless communication system, usually, frequency resources are assigned to each system statically, that is, the frequency resources assigned to each system are not adjustable. In order to effectively utilize the frequency resources and time resources of a wireless communication system, it has been proposed to assign the frequency resources dynamically. For example, such a technique is disclosed in “Dynamic Spectrum Sharing Methods for Cellular Radio Systems” Proc. Virginia Tech's 14th Symposium on Wireless Personal Communications, 2004” (hereinafter, referred to as “reference 1”).
The dynamic assignment of the frequency resources involves searching for unused frequency bands, dynamically assigning the frequency resources, and carrying out communications. In this way, signals of various frequency bandwidths are assigned to the unused frequency bands, thus the unused frequency bands are reduced, and overall frequency utilization efficiency is improved.
It has been further studied to improve the method of dynamic assignment of the frequency resources to allow a part or all of signal bands in the frequency domain of plural communication systems to be overlapped so that frequency utilization efficiency can be further improved. In this case, when signal bands of different communication systems are overlapped with each other, interference may occur, and performance of signal detection may be degraded. To solve this problem, for example, in the method of dynamic assignment of the frequency resources as disclosed in reference 1, it has been studied to overlap signals to an extent such that signal detection is not affected at the signal reception side.
In this method of dynamically assigning the frequency resources, in order to detect the vacant frequency bands, a method similar to a spectrum analyzer is used.
FIG. 1 is a block diagram illustrating a method of dynamically assigning frequency resources by using a spectrum analyzer.
As shown in FIG. 1, a spectrum analyzer is used to analyze spectra of received signals to detect the vacant frequency bands.
However, the above techniques in the related art suffer from the following problems.
As described above, in the method of analyzing the spectra of the received signals after detection of the vacant frequency bands, if the signal bands of plural communication systems are overlapped, it is difficult to correctly detect the signal bands of plural wireless communication systems.
FIG. 2 is a diagram illustrating the method of dynamically assigning the frequency resources, which allows co-existing of plural wireless communication systems in the same frequency band.
For example, as shown in FIG. 2, assume signals of a wireless communication system A, which have a narrower signal band, and signals of a wireless communication system B, which exist in the whole frequency band, and the method of dynamically assigning the frequency resources is utilized in the systems.
In this case, the signals of the wireless communication system A are overlapped in the signal band of the wireless communication system B. For example, when there are two or more antennae for receiving signals, the received signals can be easily decomposed on the receiver side, and the performance of signal detection is not degraded.
In other words, when utilizing the method of dynamically assigning the frequency resources as shown in FIG. 2, signals of two different wireless communication systems can be overlapped in the same signal band to perform communications without degrading the performance of signal detection. In this case, based on the same thoughts, a region (1) in FIG. 2, namely, a portion of the signal band of the wireless communication system A not overlapping with the signal band of the wireless communication system B can be shared by other wireless communication systems.
However, when using the spectrum analyzer to analyze spectra of the received signals to detect the vacant frequency bands, in the example shown in FIG. 2, in which the method of dynamically assigning the frequency resources is used, if the power spectrum density of the signals of the wireless communication system B is not sufficiently large compared to the power spectrum density of the signals of the wireless communication system A, it is difficult to detect the co-existing situation of two different wireless communication systems, and thus, it is difficult to detect that the region (1) is a vacant frequency band.